A revised, phylogenetically-based concept of Ceropegia (Apocynaceae)

Abstract

Recent phylogenetic reconstructions in the Ceropegieae (Apocynaceae-Asclepiadoideae) show that the 357 species of highly succulent stapeliads and four lineages of the 141 species of Brachystelma R.Br. ex Sims are nested within the 219 species of Ceropegia L.The stapeliads, shown convincingly to be nested within Ceropegia, are primarily characterized by their non-climbing, highly succulent, tuberculate stems with fleshy flowers with a mostly short corolla-tube. However, highly succulent, tuberculate stems are not restricted to the stapeliads and are present in four lineages of Ceropegia. Furthermore, tubular flowers are also found among the stapeliads and are not restricted to Ceropegia. Since a slender, tubular corolla is extremely homoplasious within Brachystelma, Ceropegia and the stapeliads, we move away from this as defining Ceropegia to recognize some sections in which there is a range from slender, tubular flowers to almost flat flowers.To re-establish a monophyletic Ceropegia, we propose a new classification in which Brachystelma and all genera of the stapeliads are placed in a greatly enlarged Ceropegia. This new concept of Ceropegia is defined by the lack of hard, wiry roots, the softly fleshy tissue of the peduncles and pedicels, the absence of any corolline corona, the presence of two well-developed series of the staminal corona and the presence of a compitum in the style-head leading to the fertilization of both ovaries. We transfer the species of Brachystelma into several sections of Ceropegia and reduce the 31 stapeliad genera to sections of Ceropegia, after which Ceropegia has 63 sections. Sect. Chamaesiphon H.Huber is the largest with 115 species, two sections among the stapeliads each contain over 50 species but the remaining sections are mostly considerably smaller. We provide diagnostic descriptions, lists of included species and distributions for each of the subdivisions that we recognise. Over 400 new combinations are made in Ceropegia.